I'm trying to get familiar with boost::iostream, so in a example program I'm writing, I want to read a text from a file and write it to file. I would use my inherited class from file_source/file_sink as device to read/write. In the read method, my class needs to add each character with one and write method needs to subtract one from each character. First of all, I want to make sure that the reading part of the program works properly so you can see the code as follow: #include <boost/iostreams/stream.hpp>#include <fstream>#include "MyFileSource.h"#include <iostream>using namespace std;using namespace boost::iostreams;int main(){ MyFileSource<char> fileSource("source.txt"); stream<MyFileSource<char>> myStream(fileSource); std::cout << myStream.rdbuf(); fileSource.close(); } and my inherited source device code is as follow: template <typename charType>class MyFileSource : public boost::iostreams::file_source {public: MyFileSource(const std::string& path) : boost::iostreams::file_source(path) { file_path = path; if (!is_open()) open(path); seek(0, ios::end); sizeOfFile = seek(0, ios::cur); seek(0, ios::beg); buffer = new charType[sizeOfFile]; } std::streamsize read(charType*, std::streamsize) { std::streamsize readCount = boost::iostreams::file_source::read(buffer, sizeOfFile); if (readCount > 0) { std::string result(buffer, readCount); for (char& c : result) c++; finalResult = result; } return readCount; } private: string file_path; int sizeOfFile; charType* buffer; std::string finalResult; }; unfortunately, the result of *std::cout << myStream.rdbuf()* with above read method is nothing while if I delete the read method of MyFileSource class to use the read method of parent, the result will be correct. Any help will be appreciated.